From 50aeef05f9f8fdb2e56ddc201b1ae7a8d56e3233 Mon Sep 17 00:00:00 2001
From: Michael Forney <mforney@mforney.org>
Date: Sun, 24 Feb 2019 20:21:59 -0800
Subject: Use a stack of scanners

This is necessary to implement the #include directive.
---
 main.c |  4 +---
 pp.c   |  6 +++---
 scan.c | 50 +++++++++++++++++++++++++++++++++++---------------
 scan.h |  4 ++--
 4 files changed, 41 insertions(+), 23 deletions(-)

diff --git a/main.c b/main.c
index 89e0b18..d526bae 100644
--- a/main.c
+++ b/main.c
@@ -37,12 +37,10 @@ main(int argc, char *argv[])
 
 	if (argc > 1)
 		usage();
-	if (argc == 1 && !freopen(argv[0], "r", stdin))
-		fatal("open %s:", argv[0]);
 	if (output && !freopen(output, "w", stdout))
 		fatal("open %s:", output);
 
-	ppinit(argc ? argv[0] : "<stdin>");
+	ppinit(argv[0]);
 	if (pponly) {
 		while (tok.kind != TEOF) {
 			tokprint(&tok);
diff --git a/pp.c b/pp.c
index 9772499..3cb4244 100644
--- a/pp.c
+++ b/pp.c
@@ -8,7 +8,6 @@
 #include "scan.h"
 #include "token.h"
 
-static struct scanner *scanner;
 static struct token pending;
 
 static void
@@ -85,14 +84,15 @@ keyword(struct token *tok)
 void
 ppinit(const char *file)
 {
-	scanner = mkscanner(file);
+	if (scanfrom(file) < 0)
+		fatal("open %s:", file);
 	next();
 }
 
 static void
 nextinto(struct token *t)
 {
-	do scan(scanner, t);
+	do scan(t);
 	while (t->kind == TNEWLINE);
 	if (t->kind == TIDENT)
 		keyword(t);
diff --git a/scan.c b/scan.c
index e6b7d70..8db5136 100644
--- a/scan.c
+++ b/scan.c
@@ -16,10 +16,14 @@ struct buffer {
 struct scanner {
 	int chr;
 	bool usebuf;
+	FILE *file;
 	struct location loc;
 	struct buffer buf;
+	struct scanner *next;
 };
 
+static struct scanner *scanner;
+
 static void
 bufadd(struct buffer *b, char c)
 {
@@ -51,16 +55,16 @@ nextchar(struct scanner *s)
 	if (s->usebuf)
 		bufadd(&s->buf, s->chr);
 	for (;;) {
-		s->chr = getchar();
+		s->chr = getc(s->file);
 		if (s->chr == '\n')
 			++s->loc.line, s->loc.col = 1;
 		else
 			++s->loc.col;
 		if (s->chr != '\\')
 			break;
-		c = getchar();
+		c = getc(s->file);
 		if (c != '\n') {
-			ungetc(c, stdin);
+			ungetc(c, s->file);
 			break;
 		}
 		++s->loc.line, s->loc.col = 1;
@@ -337,7 +341,7 @@ again:
 		loc = s->loc;
 		nextchar(s);
 		if (s->chr != '.') {
-			ungetc(s->chr, stdout);
+			ungetc(s->chr, s->file);
 			s->loc = loc;
 			s->chr = '.';
 			return TPERIOD;
@@ -372,32 +376,48 @@ again:
 	}
 }
 
-struct scanner *
-mkscanner(const char *file)
+int
+scanfrom(const char *name)
 {
 	struct scanner *s;
+	FILE *file;
 
+	if (name) {
+		file = fopen(name, "r");
+		if (!file)
+			return -1;
+	} else {
+		file = stdin;
+		name = "<stdin>";
+	}
 	s = xmalloc(sizeof(*s));
+	s->file = file;
 	s->buf.str = NULL;
 	s->buf.len = 0;
 	s->buf.cap = 0;
 	s->usebuf = false;
-	s->loc.file = file;
+	s->loc.file = name;
 	s->loc.line = 1;
 	s->loc.col = 0;
+	s->next = scanner;
+	scanner = s;
 	nextchar(s);
-
-	return s;
+	return 0;
 }
 
 void
-scan(struct scanner *s, struct token *t)
+scan(struct token *t)
 {
-	t->loc = s->loc;
-	t->kind = scankind(s);
-	if (s->usebuf) {
-		t->lit = bufget(&s->buf);
-		s->usebuf = false;
+	for (;;) {
+		t->loc = scanner->loc;
+		t->kind = scankind(scanner);
+		if (t->kind != TEOF || !scanner->next)
+			break;
+		scanner = scanner->next;
+	}
+	if (scanner->usebuf) {
+		t->lit = bufget(&scanner->buf);
+		scanner->usebuf = false;
 	} else {
 		t->lit = NULL;
 	}
diff --git a/scan.h b/scan.h
index eaf3c6d..ebfd513 100644
--- a/scan.h
+++ b/scan.h
@@ -1,4 +1,4 @@
 struct token;
 
-struct scanner *mkscanner(const char *file);
-void scan(struct scanner *, struct token *);
+int scanfrom(const char *file);
+void scan(struct token *);
-- 
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